mingw_strbuf_realpath(): handle case of non existent last path component

git often requests `strbuf_realpath(path + "/.git")`, where "./git" does
not yet exist on disk.

This causes the following to happen:
1. `mingw_strbuf_realpath()` fails
2. Non-mingw `strbuf_realpath()` does the work
3. Result of `strbuf_realpath()` is slightly different, for example it
   will not normalize the case of disk/folder names
4. `needs_work_tree_config()` becomes confused by these differences
5. clone adds `core.worktree` setting

This in turn causes various problems, for example:
1. Repository folder can no longer be renamed/moved without breaking it
2. Using the repository on WSL (Windows Subsystem for Linux) doesn't
   work, because it has windows-style path saved

This fixes #2569

Co-Authored-By: Johannes Schindelin <[email protected]>
Signed-off-by: Alexandr Miloslavskiy <[email protected]>

Author: SyntevoAlex

compat/mingw.c

@@ -1293,13 +1293,38 @@ char *mingw_strbuf_realpath(struct strbuf *resolved, const char *path)
 	HANDLE h;
 	DWORD ret;
 	int len;
+	const char *last_component = NULL;
 
 	if (xutftowcs_path(wpath, path) < 0)
 		return NULL;
 
 	h = CreateFileW(wpath, 0,
 			FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE, NULL,
 			OPEN_EXISTING, FILE_FLAG_BACKUP_SEMANTICS, NULL);
+
+	/*
+	 * strbuf_realpath() allows the last path component to not exist. If
+	 * that is the case, now it's time to try without last component.
+	 */
+	if (h == INVALID_HANDLE_VALUE &&
+	    GetLastError() == ERROR_FILE_NOT_FOUND) {
+		/* cut last component off of `wpath` */
+		wchar_t *p = wpath + wcslen(wpath);
+
+		while (p != wpath)
+			if (*(--p) == L'/' || *p == L'\\')
+				break; /* found start of last component */
+
+		if (p != wpath && (last_component = find_last_dir_sep(path))) {
+			last_component++; /* skip directory separator */
+			*p = L'\0';
+			h = CreateFileW(wpath, 0, FILE_SHARE_READ |
+					FILE_SHARE_WRITE | FILE_SHARE_DELETE,
+					NULL, OPEN_EXISTING,
+					FILE_FLAG_BACKUP_SEMANTICS, NULL);
+		}
+	}
+
 	if (h == INVALID_HANDLE_VALUE)
 		return NULL;
 
@@ -1314,6 +1339,13 @@ char *mingw_strbuf_realpath(struct strbuf *resolved, const char *path)
 	if (len < 0)
 		return NULL;
 	resolved->len = len;
+
+	if (last_component) {
+		/* Use forward-slash, like `normalize_ntpath()` */
+		strbuf_addch(resolved, '/');
+		strbuf_addstr(resolved, last_component);
+	}
+
 	return resolved->buf;
 
 }

t/t5601-clone.sh

@@ -68,6 +68,13 @@ test_expect_success 'clone respects GIT_WORK_TREE' '
 
 '
 
+test_expect_success CASE_INSENSITIVE_FS 'core.worktree is not added due to path case' '
+
+	mkdir UPPERCASE &&
+	git clone src "$(pwd)/uppercase" &&
+	test "unset" = "$(git -C UPPERCASE config --default unset core.worktree)"
+'
+
 test_expect_success 'clone from hooks' '
 
 	test_create_repo r0 &&